1. Field of the Invention
The invention relates in general to a successive approximation (SAR) analog-to-digital converter and an analog-to-digital conversion method thereof, and more particularly to an SAR analog-to-digital converter using the capacitive digital-to-analog conversion circuit and an analog-to-digital conversion method thereof.
2. Description of the Related Art
Conventionally, the successive approximation (SAR) has been used and widely applied in various fields of application. In general, the SAR analog-to-digital converter comprises an SAR control unit, a digital-to-analog conversion unit and a comparison unit. The comparison unit compares the inputted analog voltage with the reference voltage provided by the digital-to-analog conversion unit to obtain a comparison result. The SAR control unit determines the most significant bit (MSB) of the converted digital value with reference to the comparison result and adjusts the level of the reference voltage according to the MSB. The remaining bits can be converted by repeating the above operation. The SAR analog-to-digital converter can convert the inputted analog voltage to obtain the converted digital value.
In general, the digital-to-analog conversion unit of the SAR analog-to-digital converter is implemented by a capacitive digital-to-analog converter. According to existing technologies, the numeric accuracy of the capacitance is associated with the magnitude of the capacitance, and the larger the capacitance is, the higher the capacitance accuracy the capacitor has. The conventional method of increasing the capacitance accuracy to assure the linearity of the capacitive analog-to-digital converter is implemented by increasing the capacitance or area of each capacitor of the capacitive analog-to-digital converter.